X-band pulsed capability will be added to the extensive assortment of electron magnetic resonance instrumentation at the University of Illinois at Urbana/Champaign. This will provide the large and strong biomedical research community on this campus, including the nine named major- user groups, with a much needed state-of-the art tool for structural biology. The instrument will be sited in Illinois EPR Research Center (IERC) space within the School of Chemical Sciences and will be operated and managed by the IERC. The instrument chosen for this upgrade is the Bruker X-band ELEXYS FT-EPR Spectrometer System, which will incorporate the existing CW Bruker 300-series EPR spectrometer. The ELEXYS E580 FT-EPR spectrometer is a new- generation state-of-the-art instrument that is capable of performing almost all types of modern CW and pulsed EPR experiments at X-band. Dr. Sergei Dikanov, who is one of the world's leading experts in advanced pulsed electron magnetic resonance and its applications to biomedical problems involving metalloproteins and radicals and who has extensive direct experience with the E580 spectrometer system, will be in direct charge of operation and maintenance and will assist all users in effective design and interpretation of their research projects using this instrumentation. The nine major user projects focus on the following topics: contrast agents for diagnostic MRI (projects #1, Prof. R.B. Clarkson, and #2, Prof. P. Petillo); protein folding intermediates (project #3, Profs. A.I. Smirnov and R.L. Belford); electron transfer in bc1 complex (Prof. A.R. Crofts and Dr. S. Dikanov); ubiquinol oxidases (Prof R.B. Gennis), metalloenzymes protein design and engineering (Prof Y. Lu); mechanisms in vitamin B12-dependent enzymes, cytochrome c oxidase, and prostaglandin synthase (Prof. W. van der Donk); protein microspheres and heme protein analogs (Prof. K.S. Suslick); and hyperthermostable archaeal Rieske-type proteins (Dr. S. Dikanov). Many other significant users are expected from both inside and outside this institution. As examples, four minor user projects are described: insulin memesis by vanadium (Prof. C. Orvig, U. British Columbia); structure-function relationships in cytochrome c P-450 systems (Prof S. Sligar, U. Illinois); structure of NO-heme complex in irreducible and neuronal NO synthases (Dr. D. Stuehr, Cleveland Clinic); coordination geometry of dinitrosyl iron complexes in monomeric, reduced dimeric, and protein-bound forms (A. Vanin, Russ. Acad. Sci.).